Adir Bamarom: the mnemonic for the trup of veAl tzeva`o

A recent addition to HebrewBooks.org is a perush on the masoretic notes on each parsha. The notes, and perush, for parshat Behaalotecha is quite short. Here it is:

What is the meaning of it? First, a quick translation.

Behaalotecha, mesorah ketanah: "VeAl Tzevao" are four, in the matter of Yehuda, Reuven, Ephraim, Dan, and they are the heads of the banners, and with a single taam. And its mnemonic of Adi"r Bamarom.

The explanation: Adi"r is an acrostic for Ephraim {aleph} Dan Yehudah Reuven. Bamarom {=above}, its explanation is that the trup of zakef is upon the word Tzevao, and this is "bamarom," for zakef is {written} above.

End Behaalotecha.

Now to explain the commentary. In the parsha, we are told all the encampments, and there are four big divisions and then listings of each tribe. Thus, we have in Bemidbar 10:

יד  וַיִּסַּע דֶּגֶל מַחֲנֵה בְנֵי-יְהוּדָה, בָּרִאשֹׁנָה--לְצִבְאֹתָם; וְעַל-צְבָאוֹ--נַחְשׁוֹן, בֶּן-עַמִּינָדָב.	14 And in the first place the standard of the camp of the children of Judah set forward according to their hosts; and over his host was Nahshon the son of Amminadab.
טו  וְעַל-צְבָא--מַטֵּה, בְּנֵי יִשָּׂשכָר:  נְתַנְאֵל, בֶּן-צוּעָר.	15 And over the host of the tribe of the children of Issachar was Nethanel the son of Zuar.
טז  וְעַל-צְבָא--מַטֵּה, בְּנֵי זְבוּלֻן:  אֱלִיאָב, בֶּן-חֵלֹן.	16 And over the host of the tribe of the children of Zebulun was Eliab the son of Helon.

Thus, there is the standard of Yehuda, and so it speaks of Degel Machanei Benei Yehuda, in pasuk 14. Encompassed with him are Yesachar and Zevulin. But for them it just says veAl tzeva, while by Yehuda is says veAl tzevao. And there are similar groupings later in the perek for Dan, Ephraim and Reuven. And the trup on this unique word is a zakef. There is a makef connecting veAl to it, so the zakef is the trup of both words. The particular trup is וְעַ֨ל־צְבָא֔וֹ, which comes out on this page in Firefox but not other browsers, so perhaps check here at mechon-mamre. This is a pashta-zakef, or kadma-zakef, or whatever you want to call it. Wickes, IIRC, considers she pashta symbol at the head to be a mere foretone. I would note that the same trup appears even on veal tzeva. Regardless, this note is probably helpful to a sefer and to a baal koreh.